This invention relates to methods of processing carbon fibers from pitchy materials.
Carbon fibers from pitchy materials or acrylic filaments are widely being used for improving the strength, modulus of elasticity and other characteristics of composites used in aerospace, leisure, sports and other industries. Since carbon fibers are basically very brittle, however, a finish is generally used in their production in order to improve cohesion of the fibers and their processability from the spinning process and to the oxidizing process.
Recently, in view of the increased demands for improvement in the characteristics of composites, higher requirements are also being imposed on the characteristics of carbon fibers which are used for these composites. As a result, there are also increased demands for a finish with superior characteristics because the characteristics of carbon fibers are strongly dependent on the finish which is used. The present invention, therefore, relates to a method of processing carbon fiber precursor from pitchy materials with which the above demands can be satisfied.
For the production of carbon fibers, it has been known to cause silicone compounds as components of a finish having characteristics such as anti-adhesion of fibers, yarn bundle cohesion and lubricity to adhere to precursor fibers before an oxidation process (as disclosed, for example, in Japanese Patent Publication Tokko 38-12375, U.S. Pat. No. 3,656,903, Japanese Patent Publication Tokkai 49-117724 and Japanese Patent Publication Tokkai 59-223315). Almost all of them that are practically effective are hydrophobic silicone compounds, and these hydrophobic silicone compounds are accordingly used either as a solution with an organic solvent or as an aqueous emulsion.
By a method of processing with a solution having an organic solvent, however, there are always problems such as fusion because organic solvents tend to melt precursor fibers although there are differences in degree. Other problems include the danger of flammability and explosion.
Methods of processing by using an aqueous emulsion are superior, on the other hand, from the points of view of workability and safety and there have been many proposals regarding the type of emulsifier to be used, its ratio, etc. as disclosed, for example, in Japanese Patent Publication Tokkai 60-181322, U.S. Pat. No. 4,603,042, European Patent 175,200 and Japanese Patent Publication Tokkai 62-156316. There are problems with the prior art finishes described above for processing as an aqueous emulsion, however, because they cannot completely satisfy the stringent modern requirements imposed on them from the points of view of production of a stable silicone emulsion, uniform application of such an emulsion onto fibers and, in particular, prevention of adhesion among fibers.